We present a rare case of sex identity disorder (Male to Female) revealing a Klinefelter syndrome, as well as its very atypical and interesting evolution in the short term under hormonotherapy with testosterone.

Mr G. is a 48-year-old who requested sex reassignment with hormonal therapy and surgical treatment at a specialist sex dysphoria clinic. The psychiatric assessment found a gender dysphoria according to DSM-5 criteria. The patient had many atypical criteria, such as infertility or learning disorders and upon examination, the specialized endocrinologist found a testicular volume of 3mL, normal axillary and pubic hair as well as disorders of the libido with erectile dysfunction. Moreover, endocrinologist found a bioavailable testosterone at 2574pg. Finally, the karyotype revealed the diagnosis of Klinefelter syndrome with a genotype: 47 XXY. Because of the patient's fluctuant ask, treatment with quarter ampoule of enanthate of testosterone every three weeks was introduced for his Klinefelter's syndrome. This treatment did not lead to aggravation of the suffering related to gender dysphoria. The patient's psychological suffering diminished and the modification of his body image modification following testosterone treatment improved Mr G.’s gender dysphoria.

Mr G.’s body, particularly through moderate gynecomastia, has enabled him to find an aesthetic benefit with partial accommodation of his Klinefelter, which has also deliberately delayed his diagnosis. This report also highlights the fact that the percentage of patients with dysphoria, which is much higher among the Klinefelter syndromes in the literature, might be due to the lack of testosterone treatment. This atypical and uncommon observation could be sought at larger scales in patients with fluctuating dysphoria. Finally and more broadly, it also recalls the importance of researching the total testosterone levels of patients suffering from dysphoria, which do not suffer from a psychiatric pathology.